Mfr radio dating
Amperex (USA) 111 Bendix 125 Du Mont 158 Eimac (Eitel-Mc Cullough, Inc) 162 Electronic Tube Corp 169 General Electric Co (USA) 188 Hytron (CBS-Hytron) 210 Machlett 231 RCA (Radio Corp of America) 274 Raytheon 280 Superior Tube Co 310 Sylvania (Hygrade Sylvania Corp) 312 Tung-Sol 322 United Electronics 323 Western Electric 336 Westinghouse 337 Zenith Radio Corp (CRT's) 343 North American Philips Corp 423 Taylor (aka Cetron-Taylor) 713 Lewis & Kaufman 738 National Electronics (also Cetron) 749 Penta Laboratories 771 Vacuum Tube Products 781 Varian Associates 809 Litton Industries 879 Electrons, Inc 935 USA (RETMA) system First number: filament voltage 0 Cold cathode (e.g. 1 0.1 - 2.0 2 2.1 - 2.9 3 3.0 - 3.9 n n.0 - n.9 Letter or letters: sequence code One or two letters to indicate the sequence code. 12AY7: Filament rating is between 12.0 - 12.9V, AY=sequence code, 7 elements. The "hole" in the top mica identifies these USA made tubes from the TUNG-SOL factory in Newark, New Jersey, USA in the 1950's.When the single character codes were used up, double character codes were introduced. THE UNITED-ELECTRIC RELABEL CODE 88-37 IS MEANINGLESS AS THEY SIMPLY RELABELED NEW OLD STOCK TUBES FROM TUNG-SOL. NO ONE MADE D-GETTER OR SQUARE-GETTER TUBES IN 1988!
If one has a general idea of the age of the piece in question, usually the decade can be divined from that.
These are codes often seen stamped on components found in US made vintage tube equipment.
This list is circa 1955, and some codes have been reassigned or added since that time.
Examples: 6SN7GT: Filament rating is between 6.0 - 6.9V, SN=sequence code, 7 elements, glass tubular envelope. I personally have researched this in the past, and have come up with the theory that JHS was chosen by Sylvania meaning Joint Havells Sylvania or J. It has plants throughout Europe, Asia, North Africa and Central and South America, and is one of the few lighting companies that produces both lamps and lighting fixtures. Founded in the early 1900s as a business that renewed burned-out light bulbs, Sylvania and its predecessor companies ultimately began producing new lamps and then vacuum tubes for the radio industry.
It was introduced during the Second World War to rationalise the previous nomenclatures maintained separately by the War Office/Ministry of Supply, Admiralty and Air Ministry/Ministry of Aircraft Production on behalf of the three armed services for CRTs, receiving and transmitting valves used in army equipments. Havells Sylvania is an international designer and manufacturer of lighting products.